Pill resistant polyamide fiber



3,050,822 Patented Aug. 28, 1962 3,050,822 Pill. REfilfiTANT PQLYAMTDE FIBER Gtto J. Matray, Concordviiie, Pa, and William H. Stine, 31:, Wilmington, Del, assignors to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed Mar. 9, 1961, Ser. No. 94,447 13 Qiaims. (Cl. 2382) This invention relates to synthetic polyarnide filaments which are particularly useful when cut or broken into staple lengths and to a process for their production.

Fibers prepared from synthetic linear polyamides have proved superior to natural fibers in many respects and are particularly noteworthy for their increased durability. However, when fibers of staple length are employed in many end uses, such as in loosely-woven fabrics, certain types of carpets, and the like, the finished article becomes unsatisfactory in appearance after short usage due to excessive pilling and fuzzing. Pilling refers to the formation of little balls of fiber on the surface of the finished article due to the entanglement of loose fibers. Less welldefined fiber entanglements are called fuzz.

There have been many attempts to eliminate pilling by various fabric and fiber treatments. However, these attempts have generally met with only limited success and, as a result, staple fibers made from the synthetic polymers are still imperfect for many end uses despite their desirable functional characteristics.

It is the most important object of the present invention to provide a polyarnide fiber which has excellent resistance to pilling and fuzzing when fabricated into finished articles but retains a high functional level in many characteristics such as durability. A further important object is to provide a process for the production of these fibers. Other objectives and advantages will become apparent from the following specification and examples.

The objects of this invention are accomplished by the production of a crimped synthetic linear polyarnide filament having weak spots in the length thereof and characterized with respect to weak spot frequency and severity by a value for the ratio T /T o no greater than 0.80, where T is the average break tenacity in grams per denier of a one-inch filament sample and T is the average tenacity determined on the minimum sample length (zero distance between the jaws of the tester). The filament may also be characterized as to weak spot severity (the extent of degradation at a weak spot) by a significant reduction in the loop toughness value and in molecular weight at the weak spots. The filament is further characterized as to weak spot severity, abrasion resistance and durability by the relationship of average molecular Weight to loop toughness and by a number average molecular weight greater than 5000. These and other fiber characterizations will be described more fully hereinafter.

The process for producing the polyarnide filaments of this invention comprises crimping the filaments in the conventional manner and then treating them with an oxidizing agent, the treatment being continued for a sufiicient period to produce spot degradation in the filament. In a preferred process embodiment, crimped filaments are treated with an aqueous solution of hydrogen peroxide and excess solution is removed as by centrifuging the treated filaments which are then heated to complete the reaction. The processed filaments should contain from 14.0% H based on the dry weight of the filaments.

For the characterization of Weak spot frequency and severity according to the above ratio T /T the break tenacity T of zero length and 1-inch samples is meas ured. Generally, twenty-five samples of each length are tested and the tenacity values averaged. After the sampics have been tested and averaged, the ratio T /T is calculated. A commercial yarn tester such as an Instron Tester is used in making the tenacity measurements. The sample length is the distance between the jaws of the tester when the sample is extended sufficiently to just remove the crimps. The rate of elongation is 60% per minute. In measuring the zero length tenacity, the jaws of the tester are butted together at the beginning of the test. It is essential, particularly in the zero length test that the jaws of the tester be accurately aligned and have smooth, firm surfaces so that there is the minimum possible slippage in the jaws. Coating the jaws of an lnstron Tester with an epoxy resin has been found effective in this regard.

In making such measurements on spot-weakened filaments or fibers, it must be recognized that there will al- Ways be some non-uniformity among the various fibers and therefore it is imperative that a considerable number of samples be tested in order that representative values be obtained. Values from a minimum of tests should be averaged and averages of 50 or more determinations may be required to obtain reasonably reproducible results.

As mentioned previously, the relationship of molecular weight to toughness provides a good indication of Weak spot severity, abrasion resistance and durability. For purposes of comparison, numerical values indicative of the relationship may be obtained from the expression where MW is the number average molecular The term loop toughness as used herein is the amount of work, in gr. cm./cm. den., required to break a fiber loop multiplied by and is determined by measuring the area under the stress-strain curve obtained When a loop of the fiber is broken in a commercial tester such as the Instron Tester. In this test both ends of a short length of fiber are fastened in one jaw of the test apparatus to form a loop. A similar length of the fiber is passed through this loop and has both of its ends fastened in the other jaw to form a second loop. One of the fibers is then broken, the rate of elongation being 60% per minute. The length of each loop, measured from the jaw to the loop center is 0.5 inch, the distance between the jaws being one inch. The test is carried out at 72% room humidity and 70 F. and the fiber is brought to equilibrium under these conditions before being tested. As mentioned previously, the loop toughness value is a characterization of Weak spot severity.

The abrasion resistance of fibers, as referred to herein, is determined by hanging 14 samples of the fiber, under a tension of 0.2 gram per denier, over a horizontally positioned abrasive rod 12 inches in length and /2 inch in diameter, rotating the rod at 200 rpm. and recording the number of revolutions required to break each individual fiber. The average value is then taken as the single fiber abrasion. The required tension may be applied to the fiber by fixing one end in a clamp positioned 2 inches horizontally from the top of the rod and attaching a weight to the other end of the filament. The abrasive rods employed in obtaining the values recorded in the examples are India Abrasive RodsCoarse- C.F. 24. Since different abrasive rods may give some difference in abrasion resistance values, comparisons should always be made using the same rod and the test fiber should always be compared with a control such as wool.

Where reported herein, relative viscosity is determined in a 0.5% solution of the polymer in meta-cresol at 25 C.

3 EXAMPLE I Polyhexamethylene adipamide having a relative viscosity of 45 is prepared and melt extruded in the conventional manner to produce a tow consisting of denier filaments. The tow is cold drawn to a draw ratio of 4.05 and then crimped mechanically by passing it first through an atmosphere of live steam to moisten the filaments and then through a stuifer box crimper where it is subjected to sufiicient pressure to provide an average of 15 crimps per inch in each filament. The crimped tow is then placed in glass fiber bags and soaked in a 16% aqueous solution of hydrogen peroxide for 30 minutes at room temperature after which it is centrifuged to remove excess solution. The centrifuged tow, containing 15% of the peroxide solution based on the dry weight of the fiber, is steamed for 1 hour at 26 p.s.i. pressure. After drying, samples of filaments are taken at random from the tow and the severity and the frequency of the weak spots determined by measuring the breaking tenacity of zero length and 1-inch samples as described above. The breaking tenacity for the 1-inch sample, T is found to be 0.86 g.p.d. and that of the zero length sample 1.45 g.p.d., giving a ratio of T /T of 0.59. The tenacity of a 1-inch sample of untreated fiber is 5.21 g.p.d. and the zero length tenacity is 5.42, giving a ratio of 0.96.

The loop toughness of filaments removed from the tow is determined as described previously using a commercial Instron Tester with an integrator attachment and found to be 6 as compared to a value of 140 for untreated fiber.

Additional samples of filaments are taken from the tow and broken in the Instrom Tester, using a 2-inch sample length. The broken ends are then clipped off at a distance of Ms inch from the point of break and these clippings collected to determine the relative viscosity. The relative viscosity of the clippings is found to be 12, which corresponds to a molecular weight of 5,900. For purposes of comparison, the relative viscosity of the entire filament is determined and found to be 17.1 which corresponds to a molecular weight of 7,600 and a molecular weight reduction at the weak spots of 22%. The value for the molecular weight to toughness expression MW5000 is 433 toughness In making the above tests, observation of the broken ends in 50 instances reveals that the break occurs at the crimp node 6 8% of the time as compared to 46% at the crimp nodes for the untreated fiber.

The abrasion resistance of filaments removed from the tow is determined as described previously and found to be 5500. A comparative test on a high-grade wool gives a value of 200.

The tow is cut into 3-inch staple in the conventional manner and processed into 2/55s yarn, Philadelphia System, using the conventional wool process. The yarn is given a singles twist of 4.5Z and a ply twist of 3.0S. The yarn is then woven into a -02. per square yard, 198 pitch (warp ends per 27-inch width) plain, velvet-weave, loop pile carpet having eight rows per inch in the warp direction, the wire height of the loom being 0.375 inch.

A section of the carpet is placed on a stairway where only down traffic is permitted and a contact-type counting device is installed at the head of the stairway to count the number of persons, or trafiic cycles, going down the stairs. For comparison, adjacent sections of untreated nylon and wool carpets of similar construction are installed. After about 5000 cycles, the appearance of the untreated nylon carpet is unacceptable due to pilling and fuzzing while that of the carpet of this invention is equivalent to the wool carpet and entirely satisfactory in this respect. After 15,000 cycles (equivalent to 2 /24 years of normal household Wear) the wool carpet is worn to the point that it is judged unacceptable in appearance by experts in the carpet field. The carpet of this invention, however, withstands more than 60,000 cycles of the fiber.

(equivalent to 10-46 years of normal household wear) before its appearance becomes unacceptable due to wear.

EXAMPLE II Crimped nylon tow having 18 crimps per inch is prepared from polymer having a relative viscosity of 47 and treated in the same manner as described in Example I, except that the concentration of peroxide in the aqueous solution is 5% and the tow after centrifuging contains based on the dry Weight of the fiber, of the peroxide solution. When break tenacity values are obtained, T is found to be 2.15 and T is 4.92 g.p.d., giving a 'T T ratio of 0.44. The loop toughness of the treated fiber is 14 as compared to a value of 147 for the untreated fiber. 72% of the breaks occur at the crimp nodes. The relative viscosity of the treated fiber is 24 which corresponds to a molecular weight of 10,500. The value for the molecular weight to toughness expression is 550. The relative viscosity in the immediate vicinity of a weak spot (Ma-inch clipping from the break point) is 15 which corresponds to a molecular weight of 6,900 and a molecular weight reduction of 34%. When the tow is cut into 3-inch staple and processed into a carpet, as described in Example I, the pilling and fuzzing performance is greatly improved as compared to a similar car-pet prepared from untreated fiber, and the durability is 4 times that of a woll carpet of similar construction.

EXAMPLE III Crimped nylon tow having 22 crimps per inch is prepared from polymer having a relative viscosity of 45 as described in Example I and treated with hydrogen peroxide as described in Example II. The T value f r this fiber is found to be 2.22 g.p.d. and the T value 2.82 g.p.d. to give a T T 0 ratio of 0.79. Observation of 50 fiber breaks reveals that 64% of the breaks occur at the crimp nodes. The fiber abrasion resistance is 3380 as compared to a value of 200 for W001. The loop toughness is 13.3 as compared to a value of 207 for untreated fiber. The relative viscosity of the fiber is 21 which corresponds to a molecular weight of 9,000. The value for the molecular weight to toughness expression is 300. The relative viscosity in the immediate vicinity of a Weak spot A-inch clipping from the break point) is 14.7 which corresponds to a molecular weight of 6700 and a molecular weight reduction of 25%. When the tow is cut into 3-inch staple and processed into a carpet, as described in Example I, the pilling and fuzzing performance is found to be satisfactory and the durability of the carpet is about 5 times that of wool.

EXAMPLE IV Crimped nylon tow having 30 crimps per inch is prepared from polymer having a relative viscosity of 46, treated with hydrogen peroxide and heated as described 1n Example I, except that the concentration of hydrogen peroxide is 5% and the tow after centrifuging contains 60% of the peroxide solution, based on the dry weight The loop toughness of the fiber after treat-- ment with peroxide and drying is found to be 15 as compared to a value of for the untreated fiber. The break tenacity for the 1-inch sample, T is 1.99 and the T value 4.96 g.p.d. to give a T /T ratio of 0.40. Observation of 50 fiber breaks reveals that 77% of the breaks occur at the crimp nodes. The relative viscosity of the fiber is 19 which corresponds to a molecular weight of 8200. The value for the molecular weight to toughness expression is 213. The relative viscosity in the immediate vicinity of a weak spot (Vs-inch clipping from the break point) is 12.3 which corresponds to a molecular weight of 6000 and a molecular weight reduction of 27%. The abrasion resistance of the fiber is 4880 as compared to 200 for wool. When the tow is cut into 3-inch staple and processed into carpet as described in Example I, the pilling and fuzzing performance is satisfactory and the EXAMPLE V Crimped nylon tow having 21 crimps per inch and a filament denier of 19 is prepared from polymer having a relative viscosity of 45, treated with hydrogen peroxide and heated as in Example I, except that the fiber is soaked in aqueous hydrogen peroxide solution followed by centrifuging for 30 minutes. After centrifuging, the treated fiber contains based on the dry weight of the fiber, of the peroxide solution. The T value for this fiber is found to be 1.19 g.p.d. and the T value 2.47 to give a ratio T /T of 0.48. Observation of 50 fiber breaks reveals that 96% occur at the crimp nodes. The relative viscosity of the fiber is 19 which corresponds to a molecular weight of 8200. The loop toughness of the fiber is 5 as compared to 155 for the untreated fiber. The value for the molecular Weight to toughness expression is 640. The fiber has an abrasion resistance of 4800 as compared to a value of 400 obtained under identical conditions on wool. The tow is cut into staple and processed into carpet as described in Example I. When the carpet is subjected to wear on a stairway, it withstands 84,000 cycles before becoming unacceptable in appearance and the pilling and fuzzing is no greater than observed on a wool carpet subjected to the same test. The wool carpet is Worn to an unacceptable degree after 24,000 cycles.

EXAMPLE V I Nylon tow having 21 crimps per inch is prepared from polymer having a relative viscosity of 45 as described in Example I. The tow is soaked in a 2% aqueous hydrogen peroxide solution for 30 minutes and then centrifuged to remove excess solution. The centrifuged toW contains 10%, based on the dry weight o-f the fiber, of the peroxide solution. The tow is then steamed as described in Example I. The T value for this fiber is 1.97 g.p.d. and the T value 2.69 to give a T T ratio of 0.73. Observation of 50 fiber breaks reveals that 100% occur at the crimp nodes. The loop toughness of the fiber is 15. The relative viscosity of the fiber is 22.9 which corresponds to a number average molecular weight of 9500. The value for the molecular weight to toughness expression is 300. The fiber abrasion resistance is 5900 as compared to 400 for wool tested under identical conditions. When the tow is cut into 3-inch staple and processed into a carpet, as described in Example I, the carpet during wear-testing exhibits greatly improved pilling and fuzzing performance as compared to a carpet prepared from untreated nylon but the level of pilling and fuzzing, although considered acceptable from a standpoint of appearance, is somewhat higher than that observed at lower toughness levels. In this connection, it is noted that the treated fibers have a toughness of which value is the upper limit of the preferred range and T T 0 ratio value of 0.73 which value approaches the critical limit. The carpet withstood over 4 times as many traffic cycles as a wool carpet, tested simultaneously, before becoming unacceptable in appearance due to wear.

EXAMPLE VII Nylon tow having 15 crimps per inch was prepared from polymer having a relative viscosity of 45 as described in Example I. The tow was soaked in a 15% aqueous hydrogen peroxide solution for minutes and then centrifuged to remove the excess liquid. The centrifuged tow contained 15% of the peroxide solution, based on the dry weight of the fiber. The tow was then steamed as described in Example I. The T value is 1.64 g.p.d. and the T value 3.39 g.p.d. to give a T /T ratio of 0.48. Observation of 50 fiber breaks reveals that 96% occur at the crimp nodes. The loop toughness of the fiber is 4.4. The relative viscosity of the fiber is 20.3 which ii corresponds to a number average molecular weight of 8700. The value for the molecular weight to toughness expression is 613. The abrasion resistance is 4750 as compared to 400 for W001 tested under indentical conditions. When the tow is cut into 3-inch staple and processed into a carpet as described in Example I, the carpet is satisfactory in appearance with respect to piliing and fuzzing during wear-testing and withstands about 4 times the amount of wear as a wool carpet tested simultaneously.

EXAMPLE VIII Nylon tow having 30 crimps per inch is prepared from polymer having a relative viscosity of 46, treated with peroxide and heated exactly as described in Example VII. The T value for this fiber is found to be 0.90 g.p.d. and the T value 1.94 g.p.d. to give a ratio T /T of 0.46. Observation of 50 fiber breaks reveals that occur at the crimp nodes. The loop toughness of the fiber is 5.2 and the abrasion resistance is 2700 as compared to a value of 200 for wool tested under indentical conditions. The relative viscosity of the fiber is 12.4 which corresponds to a number average molecular weight of 6000. The value for the molecular weight to toughness expression is 192. When the tow is cut into staple and processed into a carpet as described in Example Vii, the carpet is satisfactory with respect to pilling and fuzzing erformance when wear-tested and the durability is about- 4 times that of a wool carpet tested simultaneously.

EXAMPLE IX Polyhexamethylene adipamide was spun and drawn 4X to give a tow of 20 denier filaments having a trilobal cross section of the type described in Holland, US. 2,939,201, the modification ratio of the cross section being 2.4 and the tip radius ratio being 0.25. The tow was crimped to 12 crimps/inch in a stuffer box crimper, soaked for 30 minutes in an 11% solution of H 0 in water and centrifuged to a solution content of 10%, based on original weight of tow. The tow was placed in a pressure vessel which was evacuated for 5 minutes and then was heated for 45 minutes by steam injected internally at a pressure of 27 1bs./in. It was cut to 3-inch staple and processed to woven carpet by the procedure described in Example I.

The yarn from which the carpet was made had a tenacity of 1.23 g.p.d. and a loop toughness of 5.3.

The carpet was laid on a hallway carrying heavy foot traffic and was found to have an acceptable level of fuzzing and pilling, high resistance to wear and a durability over three times that of wool.

EXAMPLE X A 6 nylon tow having a filament denier of 15 is produced by extruding poly-e-caproarnide having a relative viscosity of 54. The tow is cold drawn to a ratio of 4.0 in the conventional manner, crimped as described in Example I and cut into 3-inch staple. The crimped staple is soaked in 15% aqueous hydrogen peroxide for 30 minutes and then centrifuged to remove the excess liquid. The centrifuged tow, containing 15% of the peroxide solution, based on the dry weight of the fiber, is then heated for 30 minutes in steam at 20 p.s.i. The T value for this fiber is 0.99 g.p.d. and the T value 1.85 g.p.d. to give a T /T ratio of 0.54. Observation of 50 fiber breaks reveals that 87% occur at the crimp nodes. The relative viscosity of the fiber is 14.6 which corresponds to a molecular weight of 7500. The loop toughness of the fiber is 6. The value for the molecular weight to toughness expression is 417. The abrasion resistance of the fiber is 6100 as compared to 400 for W001. The staple is processed into a carpet as described in Example I. The pilling, fuzzing, and durability performance were substantially as described in connection with Example I.

7 EXAMPLE XI Poly-p-xylylene azelamide having an inherent viscosity of 0.85 in meta-cresol is prepared as described by Bower in copending application Serial No. 776,417, filed November 26, 1958. The polymer is discharged from an autoclave and cut into flake as described in U.S. Patent 2,289,774. The flake is melt spun at a temperature of 300310 C. in the conventional manner to form a 6 denier per filament, 20,000 denier tow. The tow is cold drawn to a ratio of 4.0 and then crimped to produce a tow having an average of crimps per inch. The crimped tow is soaked in 20% aqueous hydrogen peroxide solution for 30 minutes and centrifuged to remove the excess liquid. The centrifuged tow retains 20% of the peroxide solution, based on the dry weight of the fiber. It is then steamed as described in Example I. The T value for the treated fiber is found to be 1.67 g.p.d. and the T value 2.74 g.p.d., to give a T /T ratio of 0.61. Observation of 50 fiber breaks reveals that 95% occur at crimp nodes. The inherent viscosity of the fiber is 0.54 which corresponds to a molecular weight of 7400. The loop toughness of the fiber is 11 as compared to a value of 96 for the untreated fiber. The value for the molecular weight to toughness expression is 218. The abrasion resistance of the fiber is 2042 as compared to a value of 100 for wool tested under identical conditions. When the tow is cut into 3-inch staple and processed into a carpet as described in Example I, the pilling, fuzzing, and durability performance were substantially as described in connection with Example I.

EXAMPLE XII Following the general procedure outlined in Example I of U.S. Patent 2,512,606, di-(p-aminocyclohexyl)methane was prepared, reacted with sebacic acid to form a salt polymerized to give a polymer having an inherent viscosity of 0.95. The polymer was melt extruded in the conventional manner at a temperature of 300 C. to form a tow of 30,000 total denier, the denier per filament being 2. The tow is hot drawn to a ratio of 3.3 and crimped as described in Example I, the tow after crimping having 30 crimps per inch on the average. The crimped tow is soaked for 30 minutes in a 20% aqueous hydrogen peroxide solution and then centrifuged to remove excess liquid. The centrifuged tow retains 20% of the peroxide solution, based on the dry weight of the fiber. The tow is then steamed as described in Example I. The T value is 1.69 g.p.d. and the T value 2.70 g.p.d. to give a T /T ratio of 0.63. Observation of 50 fiber breaks reveals that 98% occur at the crimp nodes. The inherent viscosity of the fiber is 0.76 corresponding to a molecular weight of 11,300. The loop toughness of the fiber is 20 as compared to a value of 164 for the untreated fiber. The value for the molecular weight to toughness expression is 315. The abrasion resistance of the fiber is 3300 as compared to a value of 100 for W001 tested under identical conditions. When the tow is cut into 3-inch staple and processed into socks, the pilling, fuzzing, and durability performance were substantially as described in connection with Example XIII.

EXAMPLE XIII Polyhexamethylene adipamide of relative viscosity 45 and containing 0.3% TiO as a delusterant is spun by conventional means and cold drawn to a ratio of 0.05. Individual filaments having a denier of 3 are combined in a tow of 50,000 total denier and crimped in a stuffer box to crimps per inch. This tow is cut to 2% inch staple and soaked for 1 hour at room temperature in 5% aqueous hydrogen peroxide solution containing 2 g. citric acid per liter. The staple is centrifuged until only (based on the dry weight of the fiber) of the peroxide solution remains on the fiber and heated in steam for 2 hours at 26 psi. This staple after drying has a toughness of as compared to 270 for the untreated fiber.

0 The T value is 2.66 g.p.d. and the T value 3.58 to give a, ratio T /T of 0.75. Observation of 50 fiber breaks reveals that occur at crimp nodes. The relative viscosity of the fiber is 21.1 corresponding to a molecular weight of 8900. The value for the molecular weight to toughness expression is 156.

The treated staple, as well as untreated control staple, are spun separately on the woolen system to 1/24s yarns (Philadelphia System) having a twist of 12Z. These yarns are knitted into mens socks which are compared for pilling and fuzzing by means of a wear test in which each wearer has one sock made from control yarn and one sock made from yarn of low toughness. At the end of 5 wearings, the control sock shows noticeable pilling and fuzzing; at 10 wearings this becomes objectionable and at 20 wearings the pilling and fuzzing of the control sock is very severe. In contrast, the sock made from treated staple was in very good condition at 5 and 10 wearings and showed only slight pilling after 20- wearings.

EXAMPLE XIV Yarns prepared as in Example XIII are woven into standard flannel fabrics which are tested for pilling, without brushing or shearing, in an Accelerator. In the Accelerotor test, 4 x 4 inch samples of fabric are tumbled in a small vessel having a hard rubber inner surface by means of a mechanical agitator for varying lengths of time up to minutes. At the end of the various time intervals, the control and test fabrics are examined to determined the degree of pilling and fuzzing. The performance of the test and control fabrics is shown in the table below, using a numerical scale in which 5 indicates no change in original appearance of the fabric, 2.8 is the lower limit of acceptability from the standpoint of pilling and fuzzing, and 1 is indicative of extreme pilling and fuzzing.

Table I Filling and Fuzzing Rating Time, Minutes 15 30 60 90 120 Control 3.5 2.0 1.5 1.5 1.5 Peroxide Treated 5 5 5 4. 5 4.5

EXAMPLE XV A tow of 66 nylon was spun and drawn to give a product having a trilobal cross section of the type described in Example IX and a filament denier of 15. This was steam-crimped as described in the copending applicalion of Breen and Lauterbach, Serial No. 698,103, filed November 22, 1957, to give fibers having 14 c.p.i. This tow was soaked in 19.4% H 0 solution for 40 minutes. This tow was placed in a pressure vessel which was evacuated for 5 minutes and then heated for 50 minutes under steam at 27 p.s.i. After treatment the yarn had a T value of 0.84 g.p.d. and a T of 1.26 g.p.d., a toughness of 2.8, and a relative viscosity of 12.1 corresponding to a molecular weight of 5800. The value for the molecular weight to toughness expression is 286. The tow was cut to 3-inch staple and processed to carpet by the procedure of Example I.

This carpet showed acceptable pilling and fuzzing and was not perceptibly different from carpet made from treated trilobal fibers of the same tenacity which had been crimped in a stuffer box.

As shown in the foregoing examples, the polyamide fibers of this invention may be processed into woven and knitted structures, such as carpets, socks and fabrics to give greatly improved performance with respect to fuzzing and pilling, the improvement being such that the finished article remains entirely satisfactory in appearance after extended usage. In addition, it is found that the durability of the finished article is still far superior to that of natural fiber articles, such as wool. This is particularly suprising since the loop toughness of the fiber is reduced to a level substantially below that of wool and the severe treatment given the yarn to reduce the toughness to such low levels would normally be expected to damage the fibers to such an extent that they would be of no further value for fabrication into finished articles.

In order for the fiber to perform satisfactorily in a finished textile product, it is necessary that the frequency and severity of the weak spots be adequate to permit the pills and fuzz to break off. On the other hand, excessive weakening will damage the fiber to such extent that the durability of the finished article will be inferior.

The desired balance of properties is achieved in a fiber having a T /T value no greater than 0.80 and a loop toughness in the range of from 2 to 27. A 31/ T ratio no greater than 0.80 assures that there is at least one weak spot per inch since, in substantially all of the individual T determinations made, it is observed that the breaking tenacity is significantly reduced as compared to the reduction in breaking tenacity for the Zero sample length, the average difference being at least 20%. The T value is intended to represent the average strength of the yarn between the weak spots as nearly as can be determined. It will be appreciated, of course, that the expression zero sample length indicates the minimum sample length which can be attained and that occasionally the break will occur at a weak spot so that T is apt to be slightly lower than the actual average tenacity between the weak spots. The minimum ratio which may be toler ated without excessive weakening of the fiber will of course depend on the original strength of the fiber. For instance, a fiber with an original tenacity of grams per denier might have a ratio of 0.1 while with a fiber of 2 grams per denier this ratio would not be satisfactory. For this reason, the range of satisfactory operability is best defined in terms of loop toughness as discussed below.

The ratio T T o is also indicative of the maximum number of weak spots which may be present, since with increasing numbers of Weak spots the chances of a weak spot occurring at the point of break in the T determination is enhanced. Thus, if the number of weak spots becomes excessive, the T measurements will approximate the T measurements, just as in the case of untreated fibers, and the value for the ratio will be above 0.80.

The weak spots in the fibers of this invention are of considerably lower molecular weight than the fiber as a whole. It follows from the values given in Examples IIV that the molecular weight at the weak spots of filaments which have been treated in accordance with the instant process is at least lower than the molecular weight of an intermediate length of the treated filament. Since a Ax-inch clipping is used in determining the molecular weight reduction and since the weak spot obviously does not extend throughout the clipping, it is apparent the actual percentage reduction in molecular weight would be greater than the calculated minimum value of 20%. The number average molecular weight of the whole fiber should be greater than 5000, fibers having lower molecular weights being deficient in durability when processed into finished articles. 7

As indicated previously, the loop toughness of the treated fiber should be in the ran e of 2 to 27 and preferably in the range of 2 to 15. It is also a prerequisite to acceptable functional performance that the value of the molecular weight to loop toughness expression be at least 150. When this value is too low, the durability of the fiber in finished articles within the preferred toughness range of 2-15 will be lower than is desirable. In general, the higher the value, the better the fiber, the upper limit being dependent on what can be achieved practically in the production of such fibers. The values for loop toughness and the molecular Weight to loop toughness expression are both indicative of weak spot severity, i.e., of the extent of degradation at the weak spots, in filaments treated according to the instant process.

In order for the fiber to perform satisfactorily in woven or knitted structures, it must be crimped. When the crimping is done mechanically and the fiber is treated with an oxidizing agent, the introduction of weak points is facilitated since the attack is primarily at the points of deformation produced in crimping. This is supported by the observation that when fiber samples are broken, the breaks occur predominantly at the crimp node. Furthermore, uncrimped fibers cannot be satisfactorily processed on the equipment used for making most spun yarns and crimp contributes not only to reduction in pilling and fuzzing but also by way of bulkiness and softness in the spun yarn and articles fabricated therefrom. In addition, peroxide-degraded uncrimped fibers do not have the desired relationship of molecular weight to toughness, the values for the expression exhibited by uncrimped fibers usually being less than 100. While the degree of crimp which is desirable in the fiber will vary depending on the end use, at least 4 crimps are necessary for satisfactory processing and in general no more than 50 crimps would ever be found necessary. Preferably, the number of crimps is kept in the range of 8 to 25 per inch.

The crimping of the fiber may be carried out by any of the methods which are well known in the art but preferably is done mechanically. Mechanical crimping may be suitably carried out using the well-known stuifer box technique wherein a tow is fed into a chamber at a faster rate than it emerges. The fiber is usually moistened with water or steam prior to entry into the stutter box and the heat generated in compressing the wet fiber serves to plasticize the polyamide sufficiently to make the crimp permanent. Crimping may also be done by treating the fibers in a relaxed state with steam or other plasticizing fluid at a temperature above the second-order transition point as described by Breen and Lauterbach.

The preferred process for producing the fibers of this invention comprises crimping the fibers mechanically either concurrently or subsequently with a suitable oxidizing agent such as hydrogen peroxide and other peroxygen compounds, potassium permanganate, nitric acid and chromic acid. The preferred oxidizing agent is hydrogen peroxide since it leaves no undesirable residue in the fiber. The peroxide should be applied to the fiber in the form of an aqueous solution in a concentration of 1 to 20% H 0 based on the dry weight of the fiber. The fiber is then heated, preferably in steam, to complete the reaction. A steaming period of 10 to 60 minutes is usually sufficient. After soaking in peroxide solution, the excess liquid should be removed by centrifuging or other suitable method. In steaming the fiber, passage of the steam through the mass of fiber is hindered by the evolution of gaseous products, CO and CO due to the reaction of the H 0 with the fiber and oxygen arising from the decomposition of H 0 This difiiculty may be largely overcome by introducing steam into the center of the fiber mass, e.g., into the center of the centrifuge basket, to sweep out the gases and permit more uniform heating.

Another method of treating the fiber in staple form with aqueous peroxide, is to place the staple in a heated vessel which is rotated to tumble the staple. The aqueous hydrogen peroxide solution is then sprayed on the staple and heat is applied to complete the reaction. The percentage H 0 remaining in the fiber after soaking in aqueous H 0 solution and removal of excess liquid as described in the examples will exceed the calculated value since H 0 has a greater afiinity for the fibers than does water. For instance, fiber soaked in 5% aqueous peroxide and centrifuged as described in Example II would have a calculated H 0 content based on the dry weight of fiber of 4% whereas the true value as determined by chemical analysis is 6%.

In treating the fiber with an oxidizing agent, the timeconcentratioil-temperature relationship should be such as to reduce the loop toughness of the fiber into the range of 2 to 27, preferably 2 to 15. The exact conditions 1 1 required will, of course, vary depending upon the particular fiber selected for treatment.

The fibers of this invention may be prepared from any polyamide yarn such as, for example, those derivable from polymerizable mono-amino-carboxylic acids or their amide-forming derivatives and those derived from the reaction of diamines with dicarboxylic acids or amideforming derivatives of dibasic carboxylic acids. In addition to those set forth in the examples, other suitable polyamide fibers which may be specifically mentioned are those prepared from the polymers disclosed in US. Patents 2,071,253, 2,130,523, and 2,130,948. Interpolyamides prepared from mixtures of diamines, dibasic acids and amino acids can also be used for the practice of this invention. Likewise, melt blends'of two or more polyamides can be used as a source of suitable fibers. A further limitation is that the polyamide fibers employed must be substantially free of cross links, otherwise the abrasion resistance will be lowered excessively.

While the preferred textile product of this invention is carpets, particularly loop pile carpets, other knitted and woven structures such as blankets, sweaters, flannels, hosiery and suitings may be made to advantage from the filaments and fibers disclosed herein.

This application is a continuation-in-part of our copending application Serial No. 31,764, filed May 25, 1960, now abandoned.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A drawn oriented crimped polyamide filament having frequent, spaced, weak spots in the length thereof, said filament being characterized as to weak spot frequency and severity by a significant decrease in the break tenacity (measured in grams/denier) of filament samples as the sample length is increased from the zero length, there being at least one weak spot in substantially all of a plurality of one inch lengths.

2. The filament of claim 1 further characterized as to Weak spot severity by degradation, by a loop toughness value of from 227 and by a reduction in molecular weight of at least 20% at the weak spots, said filament having an overall molecular weight of at least 5000.

3. The filament of claim 1 further characterized as to weak spot severity by a loop toughness value of from 4-15 and by a value of at least 150 for the expression MW5000 toughness where MW is the molecular Weight of the polyamide in the filament, said filament being adapted for conversion into staple having at least one weak spot in substantially every staple length.

-4. A drawn, oriented, crimped polyamide filament having frequent, spaced, Weak spots in the length thereof, said filament being characterized as to weak spot frequency and severity by a value of less than about 0.80 for the ratio T T where T is the break tenacity of a one-inch sample and T is the break tenacity of a zerolength sample, said filament being further characterized as to weak spot severity by a loop toughness value of from 2-27.

5. The filament of claim 4 having a loop toughness value of from 415, said filament being adapted for conversion into staple having at least one weak spot in substantially every staple length.

6. The filament of claim 5 further characterized as to 12 weak spot severity by degradation and by a reduction in molecular weight of at least 20% at the Weak spots.

7. The filament of claim 4 further characterized as to weak spot severity by a value of at least for the expression MW5000 toughness Where MW is the molecular weight of the polyamide in the filament, there being at least one weak spot in substantially every one-inch length.

8. The filament of claim 7 wherein there are at least four crimps per inch and wherein the weak spots are located predominantly at the crimp nodes.

9. Crimped polyamide tow in which the individual filaments are drawn, oriented and have frequent, spaced, weak spots in the length thereof, each filament being characterized as to Weak spot frequency and severity by a value of less than about 0.80 for the ratio T T Where T is the break tenacity of a one-inch sample and T is the break tenacity of a zero-length sample, said filaments being further characterized as to weak spot severity by a loop toughness value of from 2-27.

10. Crimped, drawn and oriented polyamide staple in which the individual staple lengths have spaced weak spots, each length being characterized as to weak spot frequency and severity by a value of less than about 0.80 for the ratio T T where T is the break tenacity of a one-inch sample and T is the break tenacity of a zerolength sample, said length being further characterized as to weak spot severity by a loop toughness value of from 227.

11. The staple of claim 10 having a loop toughness value of from 4-15 and a value of at least 150 for the expression MW5000 toughness where MW is the molecular weight of the polyamide in the staple.

12. The staple of claim 11 wherein said polyamide is taken from the group consisting of polyhexamethylene adipamide, polycaproamide, poly-p-xylylene azelamide and the polymer prepared from di-(p-aminocyclohexyl)- methane and sebacic acid.

13. The staple of claim 11 further characterized as to Weak spot severity by degradation and by a reduction in molecular weight at the weak spots of at least 20% References Cited in the file of this patent UNITED STATES PATENTS 2,217,113 Hardy Oct. 8, 1940 2,260,367 Dubeau et a1 Oct. 28, 1941 2,287,099 Hardy et al. June 23, 1942 2,370,112 Truitt Feb. 20, 1945 2,443,200 Slaughter June 15, 1948 2,647,285 Pfau Aug. 4, 1953 2,720,441 Wallace Oct. 11, 1955 2,816,349 Pamm et al Dec. 17, 1957 2,909,404- Dithmar et al Oct. 20, 1959 FOREIGN PATENTS 1,024,482 Germany Feb. 20, 1958 1,033,175 Germany July 3, 1958 1,034,133 Germany July 17, 1958 1,154,495 France Apr. 10, 1958 

1. A DRAWN ORIENTED CRIMPED POLYAMIDE FIALMENT HAVING FREQUENT, SPACED, WEAK SPOTS IN THE LENGTH THEREOF, SAID FILAMENT BEING CHARACTERIZED AS TO WEAK SPOT FREQUENCY AND SEVERITY BY A SIGNIFICANT DECREASE IN THE BREAK TENACITY (MEASURED IN GRAMS/DENIER) OF FILAMENT SAMPLES AS THE SAMPLE LENGTH IS INCREASED FROM THE ZERO LENGTH, THERE BEING AT LEAST ONE WEAK SPOT IN SUBSTANTIALLY ALL OF A PLURALITY OF ONE INCH LENGTHS. 